Recently, we identified a heat and trypsin labile substance secreted by the preovulatory human ovary in the late follicular phase of the menstrual cycle which suppressed the response of other follicles to gonadotropin stimulation. Activity of the follicular protein eluted through gel permeation chromatography with a molecular weight of 12,000-15,000; bound to matrex gel Orange A, but did not bind to Concanavalin A, and had an apparent isoelectric point of pH 4-4.5 and pH 6-6.5. This protein has been shown to have no activity in an inhibin assay (suppression of FSH from pituicyte cultures). In this application, we propose to characterize the physiologic significance of this protein. In specific: 1) To correlate the activity of the follicular protein (in vitro inhibition of aromatase) to concentrations of follicular fluid steroids and granulosa cell protein and steroids obtained from spontaneously ovulatory and anovulatory women; 2) To determine the mechanism(s) of this protein's action by assessing its effect upon key enzymes in the steroidogenic pathway; 3) To evaluate the effect of this protein on the induction of gonadotropin receptors and adenyl cyclase activity in granulosa cells; 4) To evaluate the time- and dose-response effects of follicular protein on the intact hypothalamic-pituitary-ovarian primate axis; and 5) To prepare antisera to the partially purified follicular protein in a monoclonal antibody system with sufficient specificity to establish an RIA, and then quantitate this follicular protein in ovarian compartments, ovarian vein effluent and peripheral circulation at different stages of the normal follicular and luteal phase and in patients with disorders of folliculogenesis and chronic anovulation, including polycystic ovarian disease.